This invention relates to synchronous shifting multi-range hydromechanical steering transmissions for track-laying or skid-steered wheeled vehicles having hydraulic components to provide continuously variable hydrostatic drive ratios and mechanical components whose operations are selectively controlled by clutches and brakes to cause the transmission to operate in a plurality of distinct hydrostatic and hydromechanical ranges, and wherein steering is effected by using one or more hydrostatic device to impose a speed difference between left and right transmission outputs. More specifically, the present invention relates to such transmissions having internal, integral steering resulting from the utilization of the same hydrostatic units for both drive and steer rather than from the use of separate, dedicated hydrostatic units to impose a speed differential between the left and right transmission outputs to effect steering. In particular, this invention pertains to that class of multiple range steering transmissions which also has distinctly different speed and torque ratios in the various ranges and avoids the use of clutches in the steer path.
The present invention is an improvement over the steering transmission disclosed in applicant's U.S. Pat. No. 4,485,691, entitled "Simplified Hydromechanical Steering Transmission" which, in turn, is an improvement over the steering transmission disclosed in applicant's U.S. Pat. No. 4,345,488, entitled "Hydromechanical Steering Transmission". The disclosures of these patents are specifically incorporated herein by reference.
It is a principle object of the present invention to provide an improved single major axis hydromechanical steering transmission.
Another object of the present invention is to provide a hydromechanical transmission of the above character having an improved range changing mechanism.
An additional object is to provide a hydromechanical transmission of the above-character wherein the range changing mechanism is capable of producing at least four forward speed ranges.
Another object is to provide a hydromechanical transmission of the above-character wherein the range changing mechanism is of a simplified and economical construction, and is efficient and reliable in operation.
Other objects of the invention will in part be obvious and in part appear hereinafter.